Artificial Life Viewing Activity

Teacher Notes

Extracting DNA from Bananas As discussed in the program, for something to be called living or alive, it must be able to reproduce. Cells are the functional units of living things. They reproduce, in part, by making and passing deoxyribonucleic acid (DNA) from the parent cell to the offspring cell. All DNA is made up of the same chemical bases, adenine, thymine, guanine, and cytosine. The order of the bases determines the proteins the cell makes and the functions the cell performs. In this activity, students extract DNA (and also some RNA) from bananas. They see that: • DNA is a component of living and once-living things. • DNA can be extracted and observed.

Materials:

• Extracting DNA from Bananas student handout • 1 large banana • 3/4 cups distilled water • 1 teaspoon clear, colorless (i.e., not cloudy) shampoo or liquid soap containing EDTA • 1/4 teaspoon table salt • 15 ml 91% isopropyl (i.e., rubbing alcohol) in 25 ml or 50 ml sealed test tube; chill the alcohol by placing the test tube in a beaker containing ice cubes and some water • Blender or smoothie maker • 3 16-ounce plastic cups • tape (optional) • 2 plastic spoons • 1 set of measuring spoons and a measuring cup with 1/2-cup markings • 1 #4 cone paper coffee filter • 250 ml beaker • 1 plastic pipette or medicine dropper • 1 thin glass rod

Key Terms • DNA: Deoxyribonucleic acid, which is the hereditary material in cells that contains the instructions for producing the cell and enabling it to function • Extraction: A procedure to obtain a substance by chemical or mechanical action • Filtrate: The material collected after a solution or mixture passes through a filter • Precipitate: Solid material that comes out of solution as a result of a chemical or physical change National Science Education Standards Connection

Science Standard C: Life Science

• Grades 5–8: Reproduction and Heredity • Grades 9–12: The Cell; The Molecular Basis of Heredity

Video is not required for this activity.

Artificial Life Viewing Activity

Teacher Notes (cont.)

Procedure 1. Review the procedure with students, discussing key terms and responding to any questions. Explain that crushing the bananas separates its cells and exposes them to the soap and salt. The soap helps break down cell membranes and release DNA. The salt helps bring the DNA together, and the cold alcohol helps the DNA precipitate and come out of solution so it can be collected. 2. Demonstrate the following: • Show what it means to stir gently so as not to cause the solution to froth or foam. • Demonstrate how to place the coffee filter in the cup so that the solution can pass through the filter and be collected in the cup. Leave about one to two inches between the bottom of the cup and the bottom of the filter. (Taping the filter to the cup is optional.) • Remind students to get their test tubes with alcohol only when they are ready to use them. • Remind students of the importance of following the procedure carefully. 3. Divide the class into teams. Have students gather their materials and begin their extraction. Consider keeping the blenders, the beaker with the alcohol test tubes, a gallon of distilled water, the soap, and the salt in one general area. You may also want to prepare a batch of blended bananas for the entire class and distribute the mixture to teams. Make sure students know to answer the questions at the bottom of the student sheet after finishing the extraction.

Answers to questions on student handout: 1. Describe the appearance of the DNA you extracted. The DNA will appear white and will form a clump made of string-like strands that wrap onto the glass rod. 2. Summarize the main steps involved in extracting DNA from bananas. Possible answer—We crushed the bananas to help release the DNA. We made a solution— water, soap, and salt—to free the DNA from other components. The soap breaks apart the cellular and nuclear membranes, and it releases the DNA. The salt helps the DNA strands come together. We used coffee filters to remove large particles, and we used alcohol to precipitate the DNA. DNA is not soluble in alcohol. Last, we observed our product, the DNA, on a glass rod. 3. Do you think your results would be different if you were to use a fruit or vegetable other than bananas? Explain. Since DNA is in the cells of every living organism, students could use this technique to extract DNA from any fruit or vegetable.

©2005 WGBH Educational Foundation. NOVA and NOVA scienceNOW are trademarks of the WGBH Educational Foundation. NOVA and NOVA scienceNOW are produced by the WGBH Boston Science Unit. Major funding for NOVA is provided by Google. Additional funding is provided by the Corporation for Public Broadcasting and public television viewers. Major funding for NOVA scienceNOW is provided by the National Science Foundation and the Howard Hughes Medical Institute with additional funding provided by Alfred P. Sloan Foundation and The Kavli Foundation. NOVA scienceNOW is closed captioned and described for viewers who are hearing or visually impaired by the Media Access Group at WGBH. This material is based upon work supported by the National Science Foundation under Grant No. 0229297. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Artificial Life

Student Handout

Extracting DNA from Bananas For something to be considered living, it must be able to reproduce. Cells reproduce in part by passing deoxyribonucleic acid (DNA) from parent cells to offspring cells. DNA provides a blueprint for an organism’s growth and development. Studying DNA is one way scientists learn about what is necessary for life. In this activity, you will extract and observe DNA from bananas.

Procedure 1. Put 1/2 cup of distilled water and one banana into the blender. Blend for 25 seconds, making sure the banana is completely pulverized. Pour the mixture into a beaker. 2. Mix 1 teaspoon of soap with 1/4 teaspoon of salt in a plastic cup. Add 2 tablespoons of distilled water. Stir gently to avoid creating a foam. Continue for a few minutes until the soap and salt are dissolved. 3. Add 2 tablespoons of the banana mixture to the cup containing the soap solution. Use a spoon to stir the mixture for at least 10 minutes. 4. Insert a filter into a clean plastic cup so it does not touch the bottom of the cup. If necessary, tape the sides of the filter to the cup. 5. Pour the mixture from step 3 into the filter. After 10 minutes, some liquid, called the filtrate, should have collected in the bottom of the cup. Gently stir the mixture in the filter and let it sit for another minute. Remove the filter and set it aside. 6. Get a test tube of cold alcohol. Use a pipette or eyedropper to collect your filtrate. Add it to the alcohol. 7. Place the test tube with the alcohol and filtrate in a beaker or test tube holder. Let it sit undisturbed for about four minutes. Do not shake. The white material coming out of solution as a precipitate is DNA. 8. Dip the glass rod into the tube, slowly rotating it to spool out the banana’s DNA.

Questions 1. Describe the appearance of the DNA you extracted.

2. Summarize the main steps involved in extracting DNA from bananas.

3. Do you think your results would be different if you were to use a fruit or vegetable other than bananas? Explain.

©2005 WGBH Educational Foundation. NOVA and NOVA scienceNOW are trademarks of the WGBH Educational Foundation. NOVA and NOVA scienceNOW are produced by the WGBH Boston Science Unit. Major funding for NOVA is provided by Google. Additional funding is provided by the Corporation for Public Broadcasting and public television viewers. Major funding for NOVA scienceNOW is provided by the National Science Foundation and the Howard Hughes Medical Institute with additional funding provided by Alfred P. Sloan Foundation and The Kavli Foundation. NOVA scienceNOW is closed captioned and described for viewers who are hearing or visually impaired by the Media Access Group at WGBH. This material is based upon work supported by the National Science Foundation under Grant No. 0229297. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Estimating Soil Texture By Feel

Department of Agronomy

MF-2852

The word texture describes the roughness or smoothness of an object. Soil texture is determined by feeling the soil. • Soil texture is the proportion of sand, silt, and clay in the soil. • Soil texture is considered by most soil scientists to be the single most important soil property. • Soil texture affects many land uses and cannot be changed without great cost and effort. Sand, the largest particle of the soil, is visible to the eye. It is gritty, holds little water, and is not slick or sticky when wet. Sand particles are between 2 and 0.05 millimeters in diameter. Medium-sized soil particles are called silt. Silt feels like flour or talcum powder. It holds moderate amounts of water and has a somewhat sticky feel when wet. Silt particles are between 0.05 and 0.002 millimeters in diameter. The smallest particles of soil are called clay. Most individual clay particles can only be seen with a powerful microscope. Clay feels sticky when wet, and hard when dry. Clay is more chemically active than sand and silt. Clay particles are less than 0.002 millimeters in diameter.

Figure 1. Step 1: Take a handful of soil and break it up in your hand. Add water, and knead the mixture into a ball. The mixture should have the consistency of putty or Play-Doh®. Press the ball of soil between your thumb and forefinger, and try to make a ribbon. See how long you can make the ribbon before it breaks. Measure the ribbon length. Remember, there are 2.5 centimeters in 1 inch.

Soil Judging

How to determine soil texture by feel

Laboratory analyses of soil texture are costly and take time, while feeling soil texture by hand is quick, free, and, with practice, highly accurate. The two basic steps in the texture by feel method are shown in figures 1 and 2. After completing these two steps, and following the flow chart diagram, determine the soil textural class for your soil sample. The textural triangle organizes the textures into 12 classes. Notice that the loam textures are toward the middle of the diagram, because they contain a significant amount of sand, silt, and clay. The term coarse-textured is often used for soils that are dominated by sand. Fine-textured refers to soils that are dominated by clay, and medium-textured soils are a more balanced mixture of sand, silt, and clay particles.

Why is soil texture important?

Soil texture is one of the most important properties to know how to measure, as it affects many other chemical, physical, and biological soil processes and properties such as the available water-holding capacity, water movement though the soil, soil strength, how easily pollutants can leach into groundwater, and the natural soil fertility.

Figure 2. Step 2: Take a pinch of soil from your texture ball. Place it in the palm of your hand, and add water. Rub the soil and make a muddy puddle in your palm. How gritty does this feel?

Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Soil Properties Related to Texture Water storage Water movement Power needed for digging or tillage Wind or water erosion (Ease of particle detachment) Wind or water erosion (Ease of transport) Plant nutrient storage Contaminant movement

Coarse Low Low Low High

Medium Medium Medium Medium Medium

Fine High High High Low

Low Low High

Medium Medium Medium

High High Low

Soil Textural Classes Separate Sand Silt Clay

Size (mm) 2 to 0.05 0.05 to 0.002